Chain saws have endless power driven chains carrying cutting teeth. In use, the cutting teeth become dull, thereby reducing the cutting effectiveness of the saw. The teeth must be periodically sharpened. In practice, the chain with the dull teeth is removed from the blade and replaced with a chain having sharp teeth. This is a time consuming task and requires two chains. Some chain saws are equipped with self-sharpening devices that are operable to sharpen the cutting teeth during operation of the chain.